Thermoplastic adhesives, otherwise known as “hot melt” adhesives, have been widely used in industry for various applications. For example, thermoplastic hot melt adhesives are used for carton sealing, case sealing, tray forming, pallet stabilization, nonwoven application including diaper manufacturing, and many other applications. Hot melt adhesive, in its pre-melted state (referred to herein as “particulate” hot melt adhesive), can be provided in a variety of particulate shapes and sizes, ranging from small bb-sized pieces, to larger sized pieces including pellets and chips. Adhesive material, in the form of adhesive particulate, may be supplied to the adhesive melter where it is heated and melted to a desired temperature for dispensing. Hot melt adhesives are often dispensed by systems including a dispensing gun coupled via heated hoses to an adhesive melter.
An adhesive bin may contain adhesive particulate for storage prior to melting in the adhesive melter. A transfer pump, such as a pneumatic pump, connects to the adhesive bin for moving the adhesive particulate via a hose from the adhesive bin to the adhesive melter. Pneumatic pumps generally rely on the suction of gas, such as air, entrained within gaps between individual pieces of adhesive particulate stored within the adhesive bin for moving the adhesive particulate. This gas may also be referred to as “make-up” gas. Traditionally, the adhesive particulate gravity feeds into a lower portion of the adhesive bin toward an inlet of the transfer pump and submerges a majority of the pump inlet. The transfer pump generates a vacuum at the inlet that withdraws the entrained make-up gas and adhesive particulate therein. In turn, the suction of the entrained make-up gas creates a vacuum within the gaps of the adhesive particulate that withdraws additional gas from a surrounding environment. The additional gas from the surrounding environment continuously replaces the entrained/make-up gas within the adhesive bin for moving the adhesive particulate with the transfer pump.
Larger sizes of adhesive particulate tend to form larger gaps of entrained make-up gas, while smaller sizes of adhesive particulate tend to form smaller gaps of entrained make-up gas. In this respect, the smaller sizes of adhesive particulate may more densely pack within the adhesive bin than the larger sizes of adhesive particulate. The increased density results in smaller gaps throughout the adhesive particulate for drawing entrained make-up gas from the surrounding environment. Additionally, it has been determined that if a vertical depth of the adhesive particulate above the inlet is increased, then the transfer pump expends additional energy withdrawing make-up gas through the adhesive particulate within the adhesive bin. Thus, increases in the vertical depth of densely packed adhesive particulate above the inlet reduce the efficiency of the transfer pump.
There is a need, therefore, for an adhesive bin and method for use with a transfer pump that addresses present challenges and characteristics such as those discussed above.